This invention pertains to electronic engine controls and particularly to a novel electronic timing control circuit which utilizes a single pick-up for both starting and running.
One known type of electronic spark timing advance control system is disclosed in U.S. Pat. No. 3,910,243 assigned to the same assignee as the present application. In that system, separate start and run pick-ups are used to control the ignition firing under starting and running conditions, respectively. Another type of system is disclosed in the pending U.S. application, Ser. No. 588,278, filed June 19, 1975, assigned to the same assignee as the present application.
The present invention is concerned with eliminating one of the pick-ups from a dual pick-up type system but without impairing the capability of the system to perform satisfactorily during starting and running. Attempts to eliminate one of the pick-ups from a dual pick-up system have given rise to several potential obstacles. One apparent obstacle was that with a single pick-up, the pick-up signal is given in fixed relation to the engine piston position unless provision is made for mounting the pick-up so that it may be adjusted relative to crankshaft position. Another obstacle was that battery voltage experiences a large drop due to starter motor current draw which becomes even larger under extreme cold weather conditions. Moreover, the starter motor itself generates a large amount of electrical noise which greatly reduces the signal-to-noise ratio for the pick-up signal which is already a relatively low magnitude signal because of the lower velocity during engine cranking. Where the pick-up signal is utilized in an electronic timing advance circuit to reset an integrator for the purpose of generating a reference waveform representative of instantaneous crankshaft position, the pick-up must be positioned in fixed relationship to the piston position; yet, because the pick-up is also utilized for starting, its position must be such that ignition firing during starting can be accomplished at or only slightly in advance of piston top dead center position. In order to fulfill both requirements for starting and for generating the sawtooth signal during running, the ignition firing range, during running, is in the vicinity of the peak of the sawtooth; and this means that the ignition may not fire under certain transient conditions because of inherent time constants in the system.
The present invention has overcome the foregoing obstacles and provides a single pick-up electronic spark timing control system with capabilities for both starting and running. Moreover, the invention includes one feature which prevents misfiring during transient conditions which occur during running and another feature which enables ignition firing to continue despite certain impairment of normal firing during running.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode presently contemplated in carrying out the invention.